Field
Various communication systems may benefit from improved radio signaling. For example, communication systems may benefit from selective or partial filtering of a radio signal.
Description of the Related Art
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), 4th generation (4G), or 5th generation (5G) network technology, a single radio signal frame includes a plurality Orthogonal Frequency-Division Multiplexing (OFDM) symbols. For example, in a single 4G radio signal frame includes 120 to 140 OFDM symbols. The number of symbols in the radio frame can depend on the slot format of the radio signal being used. Radio signals having OFDM symbols exhibit discontinuity between adjacent OFDM symbols. The discontinuity, for example, can be caused by the phase differences between adjacent OFDM symbols, and may lead to out of band (OOB) energy leakage.
The discontinuity in the radio signal causes the frequency response, or the adjacent channel leakage ratio (ACLR), of a transmitted signal to worsen. ACLR is the ratio of the radio resource control (RRC) filtered mean power centered on the adjacent channel frequency to the RRC filtered mean power centered on the assigned channel frequency. In other words, the ACLR is the ratio of the transmitted power to the power in the adjacent radio channel. The points of discontinuity between adjacent OFDM symbols may worsen the ACLR to a point where the ACLR threshold of 3GPP specification cannot be met without channel filtering. Channel filters are therefore used to filter all transmitted time domain samples of the OFDM symbols in the radio signal. The channel filter, which may be a complex filter such as a finite impulse response (FIR) filter, consumes a large amount of Digital Signal Processing (DSP) resources in order to filter the entire radio signal.